This application is for an electron microscope to replace outmoded equipment. The instrument of choice is the JEOL, JEM 1200EX Analytical TEMSCAN with high resolution transmission (TEM), scanning (SEM) and scanning transmission (STEM) modes, eucentric goniometer and facilities for selected area x-ray probe microanalysis. This instrument will be utilized by a multi-user core group. The projects to be undertaken require the full versatility of the microscope. 1) Cell morphology and surface structure. Macrophages and mesenchymal cells, their surface membranes, and their interactions with each other and with specific targets will be examined in relation to their function in would repair, inflammation and cellular hemeostasis. Fibroblast aging in vivo and in vitro, and the distribution of various surface molecules will be examined using specific labelling procedures. 2) Studies of collagen structure and mode of assembly. The intracellular site(s) of collagen triple helix formation will be studied. Collagen mRNA containing nascent collagen chains will be examined in the intact state and following several specific enzyme treatments. The structure of collagen fibrils will be studied, by chemically modifying exposed amino- or carboxyl-groups within fibrils, and locating modified groups from the changes in the SLS banding patterns. Specific end regions of collagen molecules will be localized in fibrils using labelled antibody techniques. The structure of basement membrane components will also be studied. 3) Bone and dentin mineralization. The location of epitaxial factors in mineralizing tissues will be examined to determine their relationship to the mineralization front and intracellular route of secretion. Selected area x-ray probe microanalysis will also be used to determine the location of collagen-bound phosphoproteins with high Ca++ affinity within mineralizing tissues. 4) Dental Materials. Studies on the corrosion of dental alloys, on retreival analysis of dental amalgams and on the development of Ti alloys and porcelains will be carried out. Stress induction at porcelain-metal interfaces will also be considered. The EDAX equipment is a prime requirement for these studies. A specific plan for control of usage, user fees, instrumental maintenance and other administrative aspects is presented.